162 



The best results would probably be obtained by extracting 

 directly with alcohol, evaporating the tincture in a partial 

 vacuum, treating the residue with water, quickly filtering and 

 estimating at once with gelatine or permanganate of potassium. 

 (Cf. 51, 52, VII. and XII.) In standardizing the solutions, 

 it may be useful to remember that, according to Giinther's 

 experiments, quercitannic acid, though differing greatly in other 

 respects from gallotannic acid, possesses the same quantitative 

 action on permanganate of potassium. It must be observed 

 that tannic acid is deposited when its solution is completely 

 saturated witn chloride of ammonium ; it is advisable, therefore, 

 when precipitating with gelatine, to follow the directions given 

 for titrating catechu-tannic acid. Quercitannic aciti is sparingly 

 soluble in ether; ferroso-ferric salts produce inky mixtures with 

 its aqueous solution; other of its properties are mentioned in 

 49, 51. The lead salt obtained by precipitation with a 

 slight excess of the acetate contains 56 to 57 per cent, of oxide, 

 the copper salt 2 9 '5 per cent. The oak-red produced artificially 

 from the tannic acid is identical with the phlobaphene that occui 

 naturally in the bark. It is likewise coloured black by iron sal 

 yields protocatechuic acid and phloroglucin when fused wil 



potash, and possesses the properties of a phlobaphene 



enumerated in 108, 160. 



The tannins of the pine, 1 lirch, many species of acacia, etc., 



which have been but little investigated, may possibly resembl 



quercitannic acid in many of their essential characters. 



Filix-tannic add - is resolved, on boiling with acids, into glue 



and red flocks of filix-red ; the latter closely resembles cinchom 



red. 



Cinchona-tannic acid 3 undergoes a similar decomposition wit 



production of cinchona-red. Its lead salt is somewhat easil] 



soluble in acetic acid. 



1 Compare Kawalier, Wiener Akad. Ber. xi. 354 et seq. ; Eochleder 

 Kawalier, ibid. xxix. 22 et seq. ; Wittstein Vierteljahresschr. f. pract. Pharm. 

 iii. 14, 1854. 



2 See Malin, Chem. Centralblatt, xii. 468, 1867. For tannaspidic acid and 

 pteritannic acid, the former of which Malin believes to be impure filix-red, see 

 Luck, ibid. 657, 676, 1851. Compare further Grabowski, Annal. d. Chem. 

 und Pharm. cxlii. 279, 1867. 



3 Compare Rembold, Annal. d. Chem. und Pharm. cxliii. 270, 1867, and 

 Schwarz, Chem. Centralblatt, 193, 1852. 



